1. Field of the Invention
The present invention relates to a drive control device for an electrically-driven extending and retracting antenna, and particularly to an antenna mounted on a vehicle such as an automobile.
2. Prior Art
Generally, extending and retracting antennas consist of multiple electrically conducting tubes of different diameters installed one inside the other which are free to slide relative to each other in the manner of a telescope. A drive control device for such antennas comrises: (a) an antenna drive mechanism which consists of a motor, a gear mechanism, a clutch mechanism, a wire feed mechanism and an antenna extension and retraction operating wire, etc., and (b) a control circuit which consists of relay contacts which are operated by an extension/retraction operating switch, a transceiver set on-off switch or an ignition switch or the like and limit switches which detect the completion of the extension or retraction operation of the antenna and turn the drive mechanism off.
In drive control devices for electrically-driven extending and retracting antennas of the abovementioned type, the antenna is extended or retracted when the motor is caused to rotate in the forward or reverse direction via the operation of switches during the extending or retracting action of the antenna. When extension or retraction of the antenna is completed, a clutch mechanism comes into play to interrupt the linkage between the motor and the antenna. Immediately afterward, a limit switch is turned off on the basis of information indicating that the extension or retraction of the antenna has been completed, cutting off the power supply to the motor. A step-advance rotary mechanism is generally used to turn off the limit switch.
FIG. 12 is a rough structural diagram of a conventional step-advanced rotary mechanism used for on-off control of the limit switch. The clutch mechanism includes a rotary plate 111 which rotates as the antenna is extended or retracted. A feeding projection 112 is formed near the circumference of the rotary plate 111. A switch gear 113 with gear teeth 114 around its circumference rotates one step as a result of the feeding action of the feeding projection 112 each time the rotary plate 111 completes one rotation. When this switch gear 113 has rotated to an angle corresponding to the amount of antenna feed that occurs during extension or retraction of the antenna, this gear turns off a limit switch (not shown in the figures).
In conventional devices constructed as described above, however, problems have been encountered such as since the limit switch is turned off when switch gear 113 has rotated a prescribed number of steps, it is extremely difficult to cause the timing of the off action of the limit switch to correspond to the point in time when the antenna has actually completed its extension or retraction. Accordingly, in most cases, the system is designed so that the limit switch is turned off when the switch gear 113 has rotated one or two extra steps beyond the calculated value. Thus, turning off of the limit switch actually lags slightly behind completion of the extension or retraction of the antenna. As shown in FIG. 13, when the antenna is extended, the pushing action of the extension and retraction operating wire 116 continues even after extension of the antenna 115 has been completed. Because of this, an unreasonable force is applied to wire 116, causing it to bend as shown in the figure. This causes damage to the wire and shortens the useful life thereof. Conversely, when retraction of the antenna 115 is completed, excessive tensile force is applied to the wire 116 which also tends to damage the wire 116 shortening the useful life thereof and causing problems.